1. Field of the Invention
The present invention is directed to a linear guiding mechanism of a zoom lens barrel. The zoom lens barrel includes a lens group that is linearly guided in an optical axis direction by a linear guiding plate. The linear guiding plate is linearly guided by at least one linear guiding groove.
2. Description of Related Art
A zoom lens camera has been provided in which a cam ring is threadedly engaged (through helicoid gears) with a stationary barrel that is fixed to a camera body, the cam ring being arranged on the interior of the stationary barrel. In the camera, a zooming operation is effected in a manner such that a plurality of lens groups are moved in an optical axis direction in a predetermined manner in accordance with the rotation of the cam ring. In such a camera, it is desirable to provide a structure in which one of the plurality of lens groups is fixed to a linear guiding plate that is guided by at least one linear guiding groove, the cam ring being rotatable with respect to the linear guiding plate. The lens group is therefore prevented from rotating with respect to the stationary barrel.
In the case that the above-mentioned linear guiding groove is formed on the stationary barrel, it is preferable to make the linear guiding groove as long as possible in the optical axis direction to accommodate the movement of the linear guiding plate and, at the same time, reduce the weight of the stationary barrel, thereby reducing the weight of the zoom lens barrel of the camera.
In the camera having the above-noted structure, it is also possible to provide a mechanism for transmitting the driving force of the motor to the cam ring. In such a mechanism, a circumferential gear is provided on an outer peripheral surface of the cam ring, and a final gear of a gear train provided on the camera body is engaged with the circumferential gear. In the camera having such a structure, if the final gear is supported on the camera body, a predetermined distance between the axes of the circumferential gear and the final gear cannot be ensured. Since the position of the stationary barrel relative to the camera body is not exact, due to limitations in the precision of the manufacturing process, the gears cannot be expected to be brought into precise engagement. Furthermore, it is likely that a certain degree of play between the cam ring and the stationary barrel is likely to exist. Therefore, when the cam ring is rotated by the rotation of the final gear, the axes of the cam ring and the stationary barrel might not be coincident, with the eccentricity being equivalent to the degree of play.